<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Boost-Extended Format String Syntax</title>
<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
<link rel="home" href="../../index.html" title="Boost.Regex 7.0.1">
<link rel="up" href="../format.html" title="Search and Replace Format String Syntax">
<link rel="prev" href="perl_format.html" title="Perl Format String Syntax">
<link rel="next" href="../ref.html" title="Reference">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
<td align="center"><a href="../../../../../../index.html">Home</a></td>
<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="perl_format.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../format.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../ref.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_regex.format.boost_format_syntax"></a><a class="link" href="boost_format_syntax.html" title="Boost-Extended Format String Syntax">Boost-Extended
      Format String Syntax</a>
</h3></div></div></div>
<p>
        Boost-Extended format strings treat all characters as literals except for
        '$', '\', '(', ')', '?', and ':'.
      </p>
<h5>
<a name="boost_regex.format.boost_format_syntax.h0"></a>
        <span class="phrase"><a name="boost_regex.format.boost_format_syntax.grouping"></a></span><a class="link" href="boost_format_syntax.html#boost_regex.format.boost_format_syntax.grouping">Grouping</a>
      </h5>
<p>
        The characters '(' and ')' perform lexical grouping, so use \( and \) if
        you want a to output literal parenthesis.
      </p>
<h5>
<a name="boost_regex.format.boost_format_syntax.h1"></a>
        <span class="phrase"><a name="boost_regex.format.boost_format_syntax.conditionals"></a></span><a class="link" href="boost_format_syntax.html#boost_regex.format.boost_format_syntax.conditionals">Conditionals</a>
      </h5>
<p>
        The character '?' begins a conditional expression, the general form is:
      </p>
<p>
        ?Ntrue-expression:false-expression
      </p>
<p>
        where N is decimal digit.
      </p>
<p>
        If sub-expression N was matched, then true-expression is evaluated and sent
        to output, otherwise false-expression is evaluated and sent to output.
      </p>
<p>
        You will normally need to surround a conditional-expression with parenthesis
        in order to prevent ambiguities.
      </p>
<p>
        For example, the format string "(?1foo:bar)" will replace each
        match found with "foo" if the sub-expression $1 was matched, and
        with "bar" otherwise.
      </p>
<p>
        For sub-expressions with an index greater than 9, or for access to named
        sub-expressions use:
      </p>
<p>
        ?{INDEX}true-expression:false-expression
      </p>
<p>
        or
      </p>
<p>
        ?{NAME}true-expression:false-expression
      </p>
<h5>
<a name="boost_regex.format.boost_format_syntax.h2"></a>
        <span class="phrase"><a name="boost_regex.format.boost_format_syntax.placeholder_sequences"></a></span><a class="link" href="boost_format_syntax.html#boost_regex.format.boost_format_syntax.placeholder_sequences">Placeholder
        Sequences</a>
      </h5>
<p>
        Placeholder sequences specify that some part of what matched the regular
        expression should be sent to output as follows:
      </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Placeholder
                </p>
              </th>
<th>
                <p>
                  Meaning
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  $&amp;
                </p>
              </td>
<td>
                <p>
                  Outputs what matched the whole expression.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $MATCH
                </p>
              </td>
<td>
                <p>
                  As $&amp;
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  ${^MATCH}
                </p>
              </td>
<td>
                <p>
                  As $&amp;
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $`
                </p>
              </td>
<td>
                <p>
                  Outputs the text between the end of the last match found (or the
                  start of the text if no previous match was found), and the start
                  of the current match.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $PREMATCH
                </p>
              </td>
<td>
                <p>
                  As $`
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  ${^PREMATCH}
                </p>
              </td>
<td>
                <p>
                  As $`
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $'
                </p>
              </td>
<td>
                <p>
                  Outputs all the text following the end of the current match.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $POSTMATCH
                </p>
              </td>
<td>
                <p>
                  As $'
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  ${^POSTMATCH}
                </p>
              </td>
<td>
                <p>
                  As $'
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $+
                </p>
              </td>
<td>
                <p>
                  Outputs what matched the last marked sub-expression in the regular
                  expression.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $LAST_PAREN_MATCH
                </p>
              </td>
<td>
                <p>
                  As $+
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $LAST_SUBMATCH_RESULT
                </p>
              </td>
<td>
                <p>
                  Outputs what matched the last sub-expression to be actually matched.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $^N
                </p>
              </td>
<td>
                <p>
                  As $LAST_SUBMATCH_RESULT
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $$
                </p>
              </td>
<td>
                <p>
                  Outputs a literal '$'
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $n
                </p>
              </td>
<td>
                <p>
                  Outputs what matched the n'th sub-expression.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  ${n}
                </p>
              </td>
<td>
                <p>
                  Outputs what matched the n'th sub-expression.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  $+{NAME}
                </p>
              </td>
<td>
                <p>
                  Outputs whatever matched the sub-expression named "NAME".
                </p>
              </td>
</tr>
</tbody>
</table></div>
<p>
        Any $-placeholder sequence not listed above, results in '$' being treated
        as a literal.
      </p>
<h5>
<a name="boost_regex.format.boost_format_syntax.h3"></a>
        <span class="phrase"><a name="boost_regex.format.boost_format_syntax.escape_sequences"></a></span><a class="link" href="boost_format_syntax.html#boost_regex.format.boost_format_syntax.escape_sequences">Escape
        Sequences</a>
      </h5>
<p>
        An escape character followed by any character x, outputs that character unless
        x is one of the escape sequences shown below.
      </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Escape
                </p>
              </th>
<th>
                <p>
                  Meaning
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  \a
                </p>
              </td>
<td>
                <p>
                  Outputs the bell character: '\a'.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \e
                </p>
              </td>
<td>
                <p>
                  Outputs the ANSI escape character (code point 27).
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \f
                </p>
              </td>
<td>
                <p>
                  Outputs a form feed character: '\f'
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \n
                </p>
              </td>
<td>
                <p>
                  Outputs a newline character: '\n'.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \r
                </p>
              </td>
<td>
                <p>
                  Outputs a carriage return character: '\r'.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \t
                </p>
              </td>
<td>
                <p>
                  Outputs a tab character: '\t'.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \v
                </p>
              </td>
<td>
                <p>
                  Outputs a vertical tab character: '\v'.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \xDD
                </p>
              </td>
<td>
                <p>
                  Outputs the character whose hexadecimal code point is 0xDD
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \x{DDDD}
                </p>
              </td>
<td>
                <p>
                  Outputs the character whose hexadecimal code point is 0xDDDDD
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \cX
                </p>
              </td>
<td>
                <p>
                  Outputs the ANSI escape sequence "escape-X".
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \D
                </p>
              </td>
<td>
                <p>
                  If D is a decimal digit in the range 1-9, then outputs the text
                  that matched sub-expression D.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \l
                </p>
              </td>
<td>
                <p>
                  Causes the next character to be outputted, to be output in lower
                  case.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \u
                </p>
              </td>
<td>
                <p>
                  Causes the next character to be outputted, to be output in upper
                  case.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \L
                </p>
              </td>
<td>
                <p>
                  Causes all subsequent characters to be output in lower case, until
                  a \E is found.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \U
                </p>
              </td>
<td>
                <p>
                  Causes all subsequent characters to be output in upper case, until
                  a \E is found.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  \E
                </p>
              </td>
<td>
                <p>
                  Terminates a \L or \U sequence.
                </p>
              </td>
</tr>
</tbody>
</table></div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 1998-2013 John Maddock<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="perl_format.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../format.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../ref.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
